The long-term goal of this proposed research is to understand the molecular genetic mechanisms of craniofacial development and of orofacial cleft pathogenesis. Orofacial clefts, including cleft lip and cleft palate, are common birth defects that affect approximately 1 in 700 live births worldwide. Individuals with facial clefts undergo extensive surgical, dental, speech and psychological therapies that usually last for many years from infancy through the teenage years. Despite the frequent occurrence and extensive costly medical treatments associated with such birth defects, the causes and the pathogenic processes that lead to cleft lip and/or cleft palate are not well understood. Recent studies in animal model systems showed that development of the face, like development of other organs, are largely controlled by genetic factors. Indeed, there is accumulating evidence that specific gene mutations are associated with orofacial clefting. We have recently found that a spontaneous mutation, named Twirler, that causes cleft lip with cleft palate in homozygous mutant mice, is associated with alteration of the Zfhx1a gene. Interestingly, the Zfhx1a gene function is required for normal craniofacial development because a targeted disruption in this gene caused craniofacial defects including cleft palate in mice. The Zfhx1a gene is evolutionarily conserved and mutations in the human homolog causes multiple developmental defects. Moreover, the Zfhx1a gene product has been shown to interact with and regulate Bmp and Tgf-beta signaling, major molecular pathways regulating normal craniofacial development and involved in cleft lip/palate pathogenesis in mice and humans. Thus, we propose to determine the exact genetic lesion and the developmental mechanisms underlying facial cleft formation in the Twirler mutant mice. We will also determine the genetic interactions of Twirler/Zfhx1a with the Bmp/Tgf- beta signaling pathways during craniofacial development. These studies will greatly increase our understanding of the pathogenic mechanisms underlying orofacial cleft formation and will lead to development of methods for better diagnosis, treatment and/or prevention of orofacial clefting.